1. Field of the Invention
This invention relates to manually operated semi-automatic pistol gripped screwdrivers which have a spring-loaded trigger for actuating rotation of a screwdriver head.
2. Background Information
Semi-automatic pistol gripped screwdrivers generally fall into three different categories. The first category is illustrated in FIG. 1. The first category as shown in FIG. 1 consists of a pistol body (10), one handle or grip 18, one sliding rotation actuator 11, a helically grooved operating rod or shaft 12, a chuck or collet 13 for holding a screwdriver bit, one trigger 14, one spring loaded pulling member 15 and a torsion spring 16. In operation the trigger 14 is pulled rearwardly thereby pushing the spring loaded pulling member 15 in a rearward direction. The spring loaded pulling member 15 is attached to the sliding rotation actuator 11 so that the rearward movement of the pulling member 15 pulls the actuator backwards along the helically grooved operating rod 12, thus actuating rotation of the collet or chuck 13. The motion of the sliding rotation activator 11 along the helically grooved operating rod causes rotation of the chuck or collet 13. A switcher 17 is provided to assure that the helically grooved operating rod and hence the head of the screwdriver rotate in the desired direction.
Screwdrivers of the first category are efficient tools but they have shortcoming due to the complexity of the components and high manufacturing costs. In particular, although the torsion spring and trigger mechanism work well together to return the trigger to its original position, the torsion spring is not sufficient because it becomes weakened through use which results in a loss of function and convenience.
A second category of semi-automatic pistol gripped screwdrivers was developed as an improvement over the first category. The improved screwdriver of the second category, shown in FIG. 2, includes a spring 19 located around the helically grooved operating rod 12 behind the sliding rotation actuator 11. Moving the trigger 20 rearwardly also moves the sliding rotation actuator backwards and compresses spring 19 whereby the compressed spring exerts a force against the sliding rotation actuator in a forward direction so that the actuator can return to the forward position; thus accomplishing the same result achieved in the screwdrivers of the first category.
The second category of screwdrivers does not have the complex structure and higher cost associated with the first category of screwdrivers. However, due to the sliding design of the trigger 20, the sliding rotation actuator 11, trigger 20 and pistol 10 cannot be assembled together tightly. Consequently the sliding rotation actuator 11 and the trigger 20 cannot be pulled at the proper position. This results in undesirable shaking, swinging and undesirable bias of the sliding rotation actuator which reduces the convenience of the whole operation.
The above-noted deficiencies prompted the development of a third category of improved practical screwdrivers as shown in FIGS. 3a and 3b. The screwdrivers of this third category differ from those of the second category because the screwdrivers of the third category further include a wing piece 21 located on both sides of the sliding rotation actuator 11. Each wing piece 22 fits into a conduction slot 22 located inside the pistol body 10 to assure that the sliding rotation actuator is maintained in the proper position during use. However this improvement only overcomes some of the deficiencies of the second category of screwdrivers.